The Section works on elucidating the interaction of (complex) carbohydrate immuno-determinants with monoclonal antibodies (MAbs). We are executing: 1. Physico-chemical studies on antibody/antigen systems (V. cholera). 2. The synthesis of immunodeterminants of pathogenic entero-bacteria for affinity studies, so as to evaluate procedures for conjugate- vaccine development. 3. The amino acid sequencing by cDNA technique of monoclonal immunoglobulins obtained against V. cholera., so as to elucidate their antigen-binding phenomena. Specifically, we have synthesized the methyl a-glycoside of the trisaccharide fragment of the V. Cholera Inaba series, and mono through tetrasaccharides in the V. Cholera Ogawa series. Having prepared the crystalline monosaccharide fragments representing the terminus of the O-PS of both the Ogawa and the Inaba series we were able to show that these two compounds have differing structures. In pursuing the preparation of neoglycoprotein-based immunogens for production of anti-cholera antibodies, we have synthesized a hexasaccharide fragment of the O-PS, functionalized for attachement to a protein carrier. Circular dichroism of the O-specific polysaccharide of Vibrio cholerae O1 and some related derivatives has been investigated. The study confirmed the relationship of synthetic models to the natural O-PS. The amino acid sequence of some anti S. dysenteriae type 1 antibodies have been determined by cDNA cloning. There appears to be a remarkable diversity in sequence amongst these antibodies, even when directed against the same immunogen. A detailed study has shown that thermodynamic parameters can describe the differing binding patterns ("groove" versus "cavity") that different antibodies show against the same antigen.